The 869 Jogan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan

TLDR

Northeast Japan’s fore‑arc region experiences frequent seismic activity and tsunami generation. The authors hypothesize that the 869 Jogan tsunami’s first wave formed the sand layer and that the event was larger than typical subduction‑interface tsunamis. Sediment and hydrodynamic evidence shows the 869 tsunami, likely from a magnitude 8.3 earthquake, spread over 4 km inland, deposited fine sand, and the coastal record indicates a ~1,000‑year recurrence interval. Other information: o o o o.

Abstract

The fore-arc region of northeast Japan is an area of extensive seismic activity and tsunami generation. On July 13, 869 a tsunami triggered by a large-scale earthquake invaded its coastal zones, causing extensive deposition of well-sorted fine sand over the coastal plains of Sendai and S ma. Sediment analysis and hydrodynamic simulation indicate that the tsunami inferred to be triggered by a magnitude 8.3 earthquake spread more than 4 km inland then coast. We postulate that the sand layer was developed by the tsunami ’ s first wave. Traces of largescale invasion by old tsunami as recorded in the coastal sequences of the Sendai plain show about a 1000-year reoccurrence interval. We suggest that the J gan tsunami was much larger than tsunami generated by normal earthquakes in the subduction interface. o o o o